fix: 还原 postman 导入 pathvariable 失效的问题

backend/src/main/java/io/metersphere/api/dto/parse/postman/PostmanCollection.java

@@ -9,4 +9,5 @@ public class PostmanCollection {
 
     private PostmanCollectionInfo info;
     private List<PostmanItem> item;
+    private List<PostmanKeyValue> variable;
 }

backend/src/main/java/io/metersphere/api/dto/parse/postman/PostmanUrl.java

@@ -11,5 +11,4 @@ public class PostmanUrl {
     private String protocol;
     private String port;
     private List<PostmanKeyValue> query;
-    private List<PostmanKeyValue> variable;
 }